Processes of making monohydrate form of magnesium ammonium phosphate and processes of making cigarette paper using same

ABSTRACT

Processes for producing the monohydrate form of magnesium ammonium phosphate in slurry from use of environmentally friendly reactants are described. Slurry containing the monohydrate form of magnesium ammonium phosphate can be fed directly to, and mixed with, paper making feedstock, such as feedstock for cigarette paper, without transformation of the monohydrate form to the hexahydrate form of magnesium ammonium phosphate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to U.S.Provisional Application No. 60/540,067 entitled PROCESS OF MAKINGMONOHYDRATE FORM OF MAGNESIUM AMMONIUM PHOSPHATE AND PROCESSES OF MAKINGPAPER USING SAME and filed on Jan. 30, 2004, the entire content of whichis hereby incorporated by reference.

BACKGROUND

Magnesium ammonium phosphate has been produced in solid form and is usedprimarily as a fertilizer. It is formed as a by-product in the treatmentof waste water and in the making of magnesium phosphate cements.

SUMMARY

Processes of making the monohydrate form of magnesium ammonium phosphate(“dittmarite”) are provided. The processes can produce dittmarite in anenvironmentally friendly manner.

An exemplary process comprises introducing at least magnesium,phosphorous and nitrogen into a vessel by introducing at least tworeactants into the vessel, and reacting the at least two reactants toproduce a slurry. In preferred embodiments, the solid portion of theslurry contains a high percentage of dittmarite.

Embodiments of processes of making paper, such as cigarette paper, usedittmarite containing slurries produced by reacting environmentallyfriendly non-caustic reactants. An exemplary process comprises combiningthe slurry with paper making feedstock in a paper making process. Theslurry is preferably maintained under conditions that substantiallyprevent the transformation to struvite before it is combined with thepaper making feedstock.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary apparatus for practicing embodiments ofprocesses that produce slurries comprising the monohydrate form ofmagnesium ammonium phosphate (“dittmarite”) from environmentallyfriendly reactants and which feed the slurries to a cigarette papermaking process.

FIG. 2 shows exemplary thermogravimetric analysis (TGA) and derivative(DTGA) curves determined for a sample removed from a reactor vesselafter four minutes.

FIG. 3 shows exemplary TGA and DTGA curves determined for a sampleremoved from a reactor vessel after thirty minutes.

FIG. 4 illustrates an exemplary apparatus for practicing embodiments ofprocesses that produce dittmarite-containing slurries, which can be fedto a cigarette paper making process, or to a drying process.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary embodiments of processes of making magnesium ammoniumphosphate (also referred to herein as “AMP”) are described. Themonohydrate form of AMP (NH₄MgPO₄.H₂O, or “dittmarite”) can be producedby the processes.

Exemplary embodiments of the processes produce dittmarite by reactingenvironmentally friendly reactants, without using reactants likephosphoric acid that are used in known processes. The processes canproduce dittmarite directly from the reaction of the environmentallyfriendly reactants. The dittmarite can have high purity.

Processes of making cigarette paper by producing dittmarite, and thencombining the dittmarite with paper making feedstock in a paper makingprocess, are described. These processes can utilize dittmarite in slurryform produced by reacting environmentally friendly reactants, byembodiments of the above-described processes. The dittmarite can be feddirectly from the reactor vessel to the paper making process.

Dittmarite can transform to struvite below certain temperatures. Bycombining the as-produced dittmarite, while in slurry form and at asufficiently high temperature, with the paper making feedstock in apaper making process, potential phase changes from dittmarite tostruvite can preferably be substantially eliminated. Embodiments of theprocesses can reduce, and preferably substantially prevent, theoccurrence of such phase changes by maintaining dittmarite in a slurryform at a sufficiently high temperature until it is combined with papermaking feedstock.

In some embodiments of the processes, the as-produced dittmarite inslurry form can first be converted to a dried form of dittmarite. Thedried magnesium ammonium phosphate can be stored and then reslurriedwhen needed for later use. The reslurried magnesium ammonium phosphatecan be combined with paper making feedstock in a paper making process,or used for other purposes.

Production of Dittmarite Slurries Using Environmentally FriendlyReactants

Current commercial processes for producing magnesium ammonium phosphatereact magnesia and/or magnesium hydroxide, ammonium hydroxide and/oranhydrous ammonia, and phosphoric acid. Ammonium hydroxide, anhydrousammonia, and phosphoric acid each pose environmental and safety issues.In addition, a strongly exothermic reaction occurs when phosphoric acidis added to the basic magnesium hydroxide mixture. Consequently, currentprocesses that utilize these reactants require added safety precautions,which introduce added costs, handling procedures, and require specialpermits for practicing the processes.

Embodiments of processes of producing magnesium ammonium phosphate byreacting environmentally friendly reactants can overcome these problems.Exemplary embodiments of the processes do not utilize phosphoric acid,but rather utilize phosphate. Consequently, problems associated withusing phosphoric acid are avoided.

Exemplary embodiments of the processes comprise introducing at leastmagnesium, phosphate and nitrogen into a vessel in which magnesiumammonium phosphate is to be produced. These components are reacted toproduce a slurry containing magnesium ammonium phosphate.

Magnesium, phosphate and nitrogen can be introduced into the vessel inany suitable form or manner. For example, magnesium, phosphate andnitrogen can be provided by introducing at least two reactants into thevessel. In a preferred embodiment, the at least two reactants include atleast one magnesium containing reactant, and at least one phosphate andnitrogen containing reactant. The at least one magnesium containingreactant is preferably magnesium hydroxide (Mg(OH)₂) and/or magnesiumoxide (MgO). However, magnesium acetate and other suitable magnesiumcompounds can be used as the magnesium containing reactant. Magnesiumacetate provides good particle size control, and by-product acetate canbe readily recovered from the product.

The at least one magnesium containing reactant is preferably supplied toa reactor vessel in the form of an aqueous slurry. Magnesium hydroxideand magnesium oxide are completely insoluble in water. Dry powders ofthese magnesium compounds can be mixed with water to provide an aqueousslurry.

The phosphate containing compound is preferably ammonium dihydrogenphosphate (NH₄H₂PO₄). Ammonium dihydrogen phosphate provides a phosphategroup (PO₄) and nitrogen for the reaction to produce magnesium ammoniumphosphate. Ammonium dihydrogen phosphate is completely soluble in water(20 g/100 g at 25° C.). Thus, the phosphate can be added to the reactorvessel in aqueous form.

Preferably, dittmarite is produced by reacting magnesium hydroxideand/or magnesium oxide with ammonium dihydrogen phosphate. The reactionis conducted at boiling temperatures. For example, the reaction betweenmagnesium hydroxide and ammonium dihydrogen phosphate is as follows:Mg(OH)₂+NH₄H₂PO₄→NH₄MgPO₄.H₂O+H₂O

Referring to FIG. 1, reactants 12 are preferably added to reactor vessel10 in aqueous form. The reactor vessel can be any suitable vesselcapable of sustaining mild pressure levels, e.g., up to at least 100psi, so that the reactants can be heated to desired elevatedtemperatures to form dittmarite 14 and to prevent the transformation ofthe dittmarite to struvite, as described below. For example, the reactorvessel 10 can include a jacket for heating and cooling, be rated forpressure operation up to at least 100 psi, have a sanitary constructionfor easy clean up, and include at least one agitator, e.g., twoagitators. For example, one agitator can scrape the reactor vessel wallsand create a uniform temperature mixture, and the second agitator cansupply high shear to break up agglomerates and control particle size. Ina preferred embodiment, the reactor vessel can be a sealable autoclave,which can be sealed to prevent exposure of the vessel contents to theambient environment.

Magnesium hydroxide and magnesium oxide are completely insoluble inwater. At least one of these compounds is preferably added to thereactor vessel in slurry form. Ammonium dihydrogen phosphate iscompletely soluble in water. Accordingly, ammonium dihydrogen phosphateis preferably added to the reactor vessel as an aqueous solution.Preferably, the magnesium hydroxide and/or magnesium oxide containingslurry is added to the reactor vessel before adding the ammoniumdihydrogen phosphate to the reactor vessel.

The solids content of the magnesium hydroxide and/or magnesium oxidecontaining slurry added to the reactor vessel 10 can be selected basedon different considerations. First, the slurry is preferably stirredboth before it is added to the reactor vessel, and after it has beenadded. If the solids concentration of the magnesium hydroxide and/ormagnesium oxide solids in water exceeds about 30 wt. %, a paste mayform, which is difficult to stir. Accordingly, the solids content of themagnesium hydroxide and/or magnesium oxide containing slurry ispreferably below 30 wt. %.

A second consideration is the desired concentration of solids in themagnesium ammonium phosphate containing slurry produced by the reaction.For example, if the magnesium ammonium phosphate containing slurry issupplied to a cigarette paper making process 18, the magnesium ammoniumphosphate containing slurry can be pumped from the reactor vesseldirectly to paper making equipment. The concentration of solids in themagnesium ammonium phosphate containing slurry can be selected toachieve desired pumping and/or mixing with other ingredients supplied tothe paper making equipment. The concentration of solids in the magnesiumammonium phosphate containing slurry preferably is no greater than about25 wt. %, more preferably no greater than 20 wt. %, to achieve desiredpumping performance.

In preferred embodiments, dittmarite is formed directly from thereaction between magnesium hydroxide and/or magnesium oxide withammonium dihydrogen phosphate. In order to preferably minimizeconversion of dittmarite to struvite in the reactor vessel, thetemperature inside the reactor vessel is preferably kept sufficientlyhigh so that struvite is thermally unstable and does not form.Preferably, the temperature inside the reactor vessel is above about 55°C., more preferably above about 60° C., and most preferably above about100° C.

The reaction of magnesium hydroxide and/or magnesium oxide with ammoniumdihydrogen phosphate is mildly exothermic. Accordingly, this reactiongenerates heat, which raises the temperature of the reactants andproduct inside the reactor vessel. The temperature inside the reactorvessel is preferably monitored during the reaction. Heat can be suppliedto the reactor vessel to maintain the temperature inside the reactorvessel sufficiently high to make struvite thermally unstable. Forexample, heat can be supplied to the reactor vessel to ensure that thetemperature is above about 55° C., more preferably above about 60° C.,and most preferably above about 100° C. during the reaction. Heat can besupplied to the reactor vessel by any suitable source.

To minimize the transformation of dittmarite formed by the reaction tostruvite, the temperature of the magnesium ammonium phosphate containingslurry in the reactor vessel is preferably maintained sufficiently highafter the reaction has occurred.

The reaction to form dittmarite is preferably performed in a sealedreactor vessel under pressure. Mild pressure is generated during thereaction at the preferred temperatures described above.

EXAMPLE

An experimental example was performed to demonstrate that dittmarite canbe produced directly in slurry form, and at a high purity level, byreacting environmentally friendly reactants by the above-describedprocesses. Particularly, magnesium hydroxide was reacted with ammoniumdihydrogen phosphate to form dittmarite having high purity.

A solution was formed by adding 50 g of ammonium dihydrogen phosphate(MAP) to 250 ml of deionized water in a container. The solution wasstirred. A slurry was formed by adding 25 g of magnesium hydroxide to183 mL of deionized water in another container. The amounts of water inthe solution and slurry were determined based on an estimated finalsolids concentration of about 16 wt. %.

The magnesium hydroxide slurry was placed in a sealed reactor vessel.The slurry was agitated in the reactor vessel and heated to boiling. Theammonium dihydrogen phosphate solution was added to the slurry in thereactor vessel. Samples were taken from the reactor vessel at intervalsof time (to monitor reaction kinetics) and dried immediately foranalysis.

The dried samples were analyzed to determine the degree of reactioncompleteness, i.e., the completeness of the reaction to formNH₄MgPO₄.H₂O, or dittmarite. Using thermogravimetric analyses (TGA), TGAcurves were generated. The weight loss contributed to the degradation ofunreacted magnesium hydroxide (Mg(OH)₂) to magnesium oxide (MgO) wasdetermined. Because some weight loss in the curve in the temperaturerange for the decomposition of magnesium hydroxide is also contributedto the degradation of magnesium ammonium phosphate, the weight loss fromthe magnesium ammonium phosphate within the same temperature range wasdetermined using a high purity magnesium ammonium phosphate. The twovalues were subtracted to obtain the true weight loss due to degradationof unreacted magnesium hydroxide. The amount of unreacted ammoniumdihydrogen phosphate was also determined.

FIG. 2 shows an exemplary TGA curve A and an exemplary DTGA curve B fora sample removed from the reactor vessel after 4 minutes. TGA curve Ashows the percentage of the starting sample weight remaining versus thetemperature to which the sample was heated. DTGA curve B shows thederivative weight, indicating the rate of change of the starting sampleweight versus temperature. DTGA curve B includes peaks 1 and 2 formedduring heating of the sample. Peak 1 relates to AMP, while peak 2relates to the degradation of Mg(OH)₂.

FIG. 3 shows an exemplary TGA curve C and an exemplary DTGA curve D fora sample removed from the reactor vessel after 30 minutes. DTGA curve Dincludes peak 3, which relates to AMP, but does not include a peakrelated to the degradation of Mg(OH)₂. DTGA curve D shows thatsubstantially no Mg(OH)₂ was present in the sample after 30 minutes.

Table 1 sets forth numerical values determined from the samples takenfrom the reactor vessel at different times. TABLE 1 Unreacted UnreactedDittmarite Time Mg(OH)₂ MAP Produced (min) (wt. %) (wt. %) (wt. %) 214.227 28.061 57.712 4 12.037 23.742 64.221 6 4.062 8.011 87.927 8 3.1176.148 90.734 10 2.323 4.582 93.096 15 1.901 3.749 94.350 20 1.333 2.63096.037 25 0.800 1.577 97.623 30 0.704 1.388 97.908

As shown in Table 1, the product formed after 30 minutes of reactioncontained about 98wt. % dittmarite, and contained substantially nomagnesium hydroxide, as described above. The example demonstrated thathigh yields of dittmarite containing slurries of a high purity ofpreferably at least 95 wt. %, and more preferably at least 97 wt. %, canbe produced by embodiments of the processes by reacting environmentallyfriendly reactants.

Production of Paper Containing Dittmarite

The monohydrate form of magnesium ammonium phosphate is the desirableform of magnesium ammonium phosphate fillers in cigarette paper.Dittmarite containing slurry produced by reacting environmentallyfriendly reactants by the above-described processes can be mixed withfeedstock of a paper making apparatus 26 (FIG. 4). In preferredembodiments, the dittmarite containing slurry is fed directly from thereactor vessel, in which it is produced, to the paper making apparatus.In order to prevent the conversion of the magnesium ammonium phosphatein the monohydrate form to the hexahydrate form, it is preferable tomaintain the as-produced slurry at a temperature above 55° C., morepreferably above 60° C., until it is incorporated into paper makingfeedstock of the paper making machine. The paper making feedstock ispreferably heated to a temperature above 60° C. This slurry temperaturecan be maintained by feeding the slurry from the reactor vessel to thepaper making machine sufficiently quickly so that the slurry does nothave time to cool down to a temperature at which dittmarite maytransform to struvite. If needed, the slurry can be heated by anysuitable heating source during feeding of the slurry to the paper makingprocess to maintain the slurry temperature above the desiredtemperature, e.g., above 60° C., to avoid any potential phasetransformation to struvite.

Feeding the hot slurry directly to the paper making machine caneliminate the need to supply additional heat to the paper makingequipment to maintain a temperature above the phase transitiontemperature of dittmarite to struvite. Accordingly, energy consumptioncan be reduced in the paper making process.

In a paper making operation, dittmarite can be supplied directly to atank in which the dittmarite is mixed with one or more components of thepaper making feedstock, preferably at a temperature and/or pressuresufficient to maintain stability of the reaction product, i.e., preventtransformation to struvite. In an exemplary cigarette paper makingprocess, the overall process steps can include:

In order to provide a desired dittmarite particle size to the papermaking equipment, as indicated in FIG. 1, the dittmarite containingslurry can be subjected to a particle size reduction process 16, such asgrinding/pulverizing, before it is introduced into the paper makingequipment. An inline grinding/pulverizing device can be installed toreduce the particle size of the dittmarite to a suitable size before itis introduced into the paper making equipment.

Alternatively, the slurry of monohydrate magnesium ammonium phosphatecan be dried to particle form (e.g., powder), and such powder can beincorporated in the paper making feedstock. The slurry is preferablymaintained above about 55° C., more preferably above about 60° C., untilthe slurry is dried. As shown in FIG. 4, the slurry can be pumped by apump 32 to a drier 30. The drier 30 can be, e.g., a spin-flash drier,which removes water from the slurry under elevated temperatureconditions. A preferred spin-flash drier (SFD) for drying the slurry toparticle form can be obtained from APV Anhydro of Tonawanda, N.Y. Oncedry, the dittmarite remains stable. If desired, the resultant powder canbe further reduced in particle size using known milling or grindingtechniques.

For paper making, the particle size of dittmarite is preferably in therange of approximately 2 μm to 8 μm, more preferably in the range of 2μm to 4 μm. As shown in FIG. 4, the dried slurry particles can besubjected to a separating step to separate the particles into anydesired size fractions. For example, the dried slurry particles and aircan be fed to a cyclone 40 to provide sized particles 42.

The cigarette making process can produce traditional cigarettes, orother less traditional cigarettes, such as cigarettes usable withelectronic smoking devices, which are described in U.S. Pat. No.6,289,898.

Thus, embodiments of the processes can conserve energy by feeding theslurry directly from the reactor vessel to the paper making equipment,without first drying and then reslurrying dried dittmarite. Producingdittmarite at the site of the paper making process can eliminate storageand transportation costs, and minimize potential transformation ofdittmarite to struvite during such storage.

Embodiments of the processes also eliminate problems associated with theuse of corrosive, dangerous reactants including phosphoric acid, such ashandling, special permit requirements, and controlling stronglyexothermic reactions.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

1. A process of making a slurry, comprising: introducing at leastmagnesium, phosphate and nitrogen into a vessel by introducing at leasttwo reactants into the vessel; reacting the at least two reactants toproduce a slurry comprising substantially dittmarite; and maintainingthe slurry at a sufficiently high temperature to substantially preventthe transformation of the dittmarite to struvite.
 2. The process ofclaim 1, wherein the slurry comprises a solids portion including atleast 95 wt. % dittmarite.
 3. The process of claim 1, wherein the atleast two reactants include (i) ammonium dihydrogen phosphate and (ii)at least one of magnesium hydroxide and magnesium oxide.
 4. The processof claim 1, wherein ammonium dihydrogen phosphate is introduced into thevessel as an aqueous solution, and at least one of magnesium hydroxideand magnesium oxide is introduced into the vessel as a slurry having asolids content below 30 wt. %.
 5. The process of claim 1, wherein the atleast two reactants include ammonium dihydrogen phosphate and magnesiumacetate.
 6. The process of claim 1, wherein the slurry has a solidscontent no greater than 20 wt. %.
 7. The process of claim 1, wherein thevessel is sealed.
 8. The process of claim 1, further comprising dryingthe slurry.
 9. The process of claim 8, wherein the drying is conductedwith a spin-flash drier.
 10. The process of claim 1, wherein the vesselis maintained at a temperature of at least about 100° C.
 11. A processof making paper, comprising: producing a slurry comprising substantiallydittmarite by the process according to claim 1; and combining the slurrywith paper making feedstock in a paper making process.
 12. The processof claim 11, further comprising reducing particle size of the dittmaritebefore combining the slurry with the paper making feedstock.
 13. Theprocess of claim 11, further comprising drying the slurry and thenreslurrying dried dittmarite before combining the slurry with the papermaking feedstock.
 14. The process of claim 11, wherein the slurry is feddirectly from the vessel to the paper making process withouttransformation of the dittmarite to the hexahydrate form of magnesiumammonium phosphate.
 15. The process of claim 11, wherein the slurry ismaintained at a temperature above a phase transition temperature ofdittmarite to a hexahydrate form of the magnesium ammonium phosphatefrom when the slurry is produced until the slurry is combined with thepaper making feedstock.
 16. The process of claim 15, wherein the slurryis maintained at a temperature of at least about 60° C. from when theslurry is produced until the slurry is combined with the paper makingfeedstock.
 17. The process of claim 16, further comprising heating theslurry to a temperature of at least about 60° C. in the vessel.
 18. Theprocess of claim 11, wherein the paper making process is a cigarettepaper making process.
 19. A process of making a slurry, comprising:introducing at least magnesium, phosphorous and nitrogen into a vesselby introducing at least two reactants into the vessel, the at least tworeactants not including phosphoric acid; reacting the at least tworeactants to produce a slurry comprising substantially dittmarite; andmaintaining the slurry at a sufficiently high temperature tosubstantially prevent the transformation of the dittmarite to struvite.20. The process of claim 19, wherein the slurry comprises a solidsportion including at least 95 wt. % dittmarite.
 21. The process of claim19, wherein the slurry has a solids content no greater than 20 wt. %.22. The process of claim 19, further comprising drying the slurry. 23.The process of claim 19, wherein the vessel is maintained at atemperature of at least about 100° C.
 24. A process of making paper,comprising: producing a slurry comprising substantially dittmarite bythe process according to claim 19; and combining the slurry with papermaking feedstock in a paper making process.
 25. The process of claim 24,further comprising reducing particle size of the dittmarite beforecombining the slurry with the paper making feedstock.
 26. The process ofclaim 24, further comprising drying the slurry and then reslurryingdried dittmarite before combining the slurry with the paper makingfeedstock.
 27. The process of claim 24, wherein the slurry is feddirectly from the vessel to the paper making process withouttransformation of the dittmarite to the hexahydrate form of magnesiumammonium phosphate.
 28. The process of claim 24, wherein the slurry ismaintained at a temperature above a phase transition temperature ofdittmarite to a hexahydrate form of the magnesium ammonium phosphatefrom when the slurry is produced until the slurry is combined with thepaper making feedstock.
 29. The process of claim 24, wherein the papermaking process is a cigarette paper making process.